The present invention relates to a method of reinforcing an optical fiber coupler manufactured by fusing and then extending a plurality of optical fibers. The optical fibers are secured to a substrate by adhesive.
Conventional optical fiber couplers are apt to change in characteristic or are easily damaged by an external force or a temperature change since they have a fine-diameter portion with an outer diameter sized in micrometers. In order to protect the conventional optical fiber coupler against an external force so as to assure that a stable characteristic is maintained, the conventional optical fiber coupler has been fixed on a reinforcing substrate having a coefficient of linear expansion substantially equal to that of quartz. A plate-like member has been used as the reinforcing substrate, as disclosed, for example, in Japanese Utility Model Unexamined Publication No. Sho. 60-4308. Further, as another example of the reinforcing substrate, a pipe-shaped member has been disclosed in Japanese Patent Unexamined Publication No. Sho-64-63907. In addition, a thermosetting or ultraviolet-setting type adhesive of an epoxy group, an urethane acrylate group, or a cyanoacrylate group has been employed as the conventional coupler fixing adhesive.
Recently, light communication lines has been promoted which has increased the use of optical fiber couplers. In this regard, however, there has been a disadvantage in that the occupation area of conventional couplers has increased and the method of accommodating excessive length of optical fibers has become complicated, since each conventional coupler is constituted by a pair of optical fibers.
Japanese Patent Unexamined Publication No. Hei-1-295211 discloses a method in which an optical fiber coupler, constituted by two optical fibers, is fixed on a reinforcing member. A plurality of such reinforcing members are accommodated in a package, and optical fibers outside the package are formed into tape-like, multiple optical fiber units. Further, Japanese Patent Unexamined Publication No. Sho-63-254406 discloses a method in which an optical fiber coupler, constituted by two optical fibers, is provided in each of a plurality of grooves of a fixing portion shaped in the form of teeth of a comb.
However, in each of the methods disclosed in the above Japanese Patent Unexamined Publication Nos. Hei. 1-295211 and Sho-63-254406, there has been a problem in that much time is required to manufacture the multiple optical fiber unit couplers by such methods because the optical fiber couplers, each constituted by two optical fibers, are densely mounted. Although a trial manufacture of a multiple optical fiber unit coupler from multiple optical fiber units has been made, a problem exits in that when the multiple optical fiber unit coupler is fixed on a reinforcing substrate, the transmission characteristic remarkably changes with a temperature change and under high humidity.